Brandon Moss (center) is mobbed by teammates who took his jersey before giving him a pie in the face for his winning homer.

Photo: Lance Iversen, The Chronicle

Brandon Moss (center) is mobbed by teammates who took his jersey...

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Coco Crisp (4), after scoring on a Moss double in the eighth, doesn't like the call when Stephen Drew is out at home plate.

Photo: Lance Iversen, The Chronicle

Coco Crisp (4), after scoring on a Moss double in the eighth,...

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Seattle Mariners' Tom Wilhelmsen, right, turns his back as Oakland Athletics' Josh Donaldson runs the bases after Donaldson hit a two-run home run in the ninth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Seattle Mariners' Tom Wilhelmsen, right, turns his back as Oakland...

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Oakland Athletics' Stephen Drew (5) is tagged out at home plate by Seattle Mariners catcher Miguel Olivo in the eighth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. Drew was attempting to score on a hit by (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Stephen Drew (5) is tagged out at home plate by...

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Seattle Mariners Franklin Gutierrez hits the wall trying to catch a a two-run home run hit by Oakland Athletics' Josh Donaldson in the ninth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Oakland Athletics' Josh Donaldson celebrates after hitting a two-run home run off Seattle Mariners' Tom Wilhelmsen in the ninth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. The Athletics won 7-4 in 10 innings. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Josh Donaldson celebrates after hitting a...

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Oakland Athletics' Josh Donaldson (20) celebrates with Josh Reddick (16) after Donaldson hit a two-run home run off Seattle Mariners' Tom Wilhelmsen in the ninth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

OAKLAND, CA - SEPTEMBER 29: Dan Straily #67 of the Oakland Athletics pitches against the Seattle Mariners during the first inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Dan Straily #67 of the Oakland...

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Oakland Athletics' Brandon Moss, right, is congratulated by teammates after hitting the game-winning three-run home run in the 10th inning of a baseball game against the Seattle Mariners on Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Brandon Moss, right, is congratulated by...

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OAKLAND, CA - SEPTEMBER 29: Josh Donaldson #20 of the Oakland Athletics catches a fly ball hit off the bat of Franklin Gutierrez #21 of the Seattle Mariners (not pictured) during the first inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Josh Donaldson #20 of the Oakland...

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OAKLAND, CA - SEPTEMBER 29: John Jaso #27 of the Seattle Mariners advances to second base ahead of a throw in front of Stephen Drew #5 of the Oakland Athletics during the second inning at O.co Coliseum on September 29, 2012 in Oakland, California. Jaso scored on the play which involved two throwing errors. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: John Jaso #27 of the Seattle Mariners...

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OAKLAND, CA - SEPTEMBER 29: Yoenis Cespedes #52 of the Oakland Athletics dives past Miguel Olivo #30 of the Seattle Mariners to score a run during the fourth inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Yoenis Cespedes #52 of the Oakland...

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OAKLAND, CA - SEPTEMBER 29: Carlos Triunfel #8 of the Seattle Mariners slides into third base ahead of tag from Josh Donaldson #20 of the Oakland Athletics in front of umpire Eric Cooper #56 during the fifth inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Carlos Triunfel #8 of the Seattle...

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OAKLAND, CA - SEPTEMBER 29: Michael Saunders #55 of the Seattle Mariners is congratulated by Justin Smoak #17 after hitting a two run home run against the Oakland Athletics during the fourth inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Michael Saunders #55 of the Seattle...

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OAKLAND, CA - SEPTEMBER 29: Yoenis Cespedes #52 of the Oakland Athletics dives into home plate to score a run against the Seattle Mariners during the fourth inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Yoenis Cespedes #52 of the Oakland...

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OAKLAND, CA - SEPTEMBER 29: Dan Straily #67 of the Oakland Athletics reacts after giving up a home run against the Seattle Mariners during the fourth inning at O.co Coliseum on September 29, 2012 in Oakland, California. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: Dan Straily #67 of the Oakland...

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OAKLAND, CA - SEPTEMBER 29: The Oakland Athletics empty the bench after a walk off three run home run hit by Brandon Moss #37 of the Oakland Athletics (not pictured) at O.co Coliseum against the Seattle Mariners on September 29, 2012 in Oakland, California. The Oakland Athletics defeated the Seattle Mariners 7-4 in 10 innings. (Photo by Jason O. Watson/Getty Images)

Photo: Jason O. Watson, Getty Images

OAKLAND, CA - SEPTEMBER 29: The Oakland Athletics empty the bench...

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Oakland Athletics' Brandon Moss celebrates as he rounds the bases after hitting the game-winning three-run walk off home in the 10th inning of a baseball game against the Seattle Mariners Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Brandon Moss celebrates as he rounds the bases...

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Oakland Athletics' Dan Straily works against the Seattle Mariners in the first inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Dan Straily works against the Seattle Mariners...

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Seattle Mariners' Jason Vargas works against the Oakland Athletics in the first inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Seattle Mariners' Jason Vargas works against the Oakland Athletics...

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Oakland Athletics' Dan Straily, right, waits for a new ball as Seattle Mariners' Michael Saunders, background, runs the bases after hitting a two-run home run off Straily in the fourth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics' Dan Straily, right, waits for a new ball as...

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Oakland Athletics third baseman Josh Donaldson misses a throw allowing Seattle Mariners' John Jaso to score in the second inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. At right is third base umpire Eric Cooper. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Oakland Athletics third baseman Josh Donaldson misses a throw...

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Seattle Mariners' Michael Saunders, right, and Justin Smoak celebrate after Saunders hit a two-run home run off Oakland Athletics' Dan Straily in the fourth inning of a baseball game Saturday, Sept. 29, 2012, in Oakland, Calif. (AP Photo/Ben Margot)

Photo: Ben Margot, Associated Press

Seattle Mariners' Michael Saunders, right, and Justin Smoak...

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Oakland Athletics' Brandon Moss watches his three-run home run in the 10th inning of a baseball game against the Seattle Mariners on Saturday, Sept. 29, 2012, in Oakland, Calif. The Athletics won 7-4. (AP Photo/Ben Margot)

Players come and go this year, or they change positions or roles, but one thing that never varies is the A's flair for the dramatic.

With Oakland down by two in the ninth and showing little offensive oomph all day, third baseman Josh Donaldson suddenly clubbed a two-run homer to tie the score.

That set the stage for the A's oh-so-familiar thrills 'n' chills script: In the 10th inning, Brandon Moss pasted a three-run homer to right off Stephen Pryor to give Oakland a 7-4 victory over the Mariners on Saturday at the Coliseum.

"Oh my goodness, it's fun any time, but when you're trying to make the playoffs and every game is so important, they don't get bigger than that," Moss said.

The A's walk-off win was their major-league-leading 14th of the season, and yes, Moss got a whipped-cream pie in the kisser for his troubles. He's well-rehearsed: He did the same thing on July 20 against the Yankees.

"I ate a lot of it this time," Moss said with a grin. "My mouth was open."

The A's have won 90 games, something no one apart from Jonny Gomes and Coco Crisp envisioned before the season, and their magic number is three with four games remaining. They could clinch Sunday with a combination of their own win, a loss by Tampa Bay and two losses by the Angels. The Angels, though, play a split double-header at Texas, and the A's players are likely to leave the ballpark well before the second game at Texas is over. So they might clinch their first postseason spot in six years and delay the celebration for a day.

Not that Oakland players are looking that far ahead. Their one-day-at-a-time talk is cliche but effective.

"There's no way to deny you feel it," Moss said of the increasing likelihood of the postseason. "It drives you; you can feel it coming. But you can't play outside yourself. Looking ahead only takes away from today."

Moss hit the first pitch he got from Pryor. He had popped up the night before against him on a fastball up so he was hoping for a fastball down Saturday - and that's what he got.

He wasn't thinking home run, and in fact, Moss said, he hit it better than he'd thought initially. Donaldson, however, was thinking nothing but driving the ball out of the park, given the situation when he stepped up against Tom Wilhelmsen.

"I was really trying to hit a home run," Donaldson said. "I don't know how else to say it."

Wilhelmsen started him off with a fastball, so Donaldson figured he might come back with a breaking pitch - which is what he got. He sent it sailing over the wall in dead center, his ninth homer of the season.

The Donaldson/Moss homer combo illustrates the A's unlikely season perfectly: Donaldson is a catcher playing third base, and he's been up and down this season. Moss, an outfielder playing first base, was signed as a minor-league free agent last winter and wasn't called up until June. He has hit 21 homers in 254 at-bats.

Moss also made a great catch to end the ninth, diving to his right for a liner by pinch-hitter Jesus Montero and stranding a Mariners runner in scoring position - potentially saving a run.

Asked how difficult the liner was to catch, Moss joked, "If I'd have seen it, I'd tell you."

Crisp, in the second day back from an eye ailment, had four hits, and he singled to open the 10th against Oliver Perez. Pryor took over to face Yoenis Céspedes with one out and walked him, bringing up Moss.

"We've experienced that before," A's manager Bob Melvin said of the last-at-bat win, "but I don't think we've had one with the magnitude of that. Donaldson's home run was epic - and for Mossy to do that there, that's a pretty dramatic win."